Wireless communication systems are widely used to provide various types of communications. For example, voice and/or data are provided by the wireless communication systems. A conventional wireless communication system provides multiple users with one or more shared resources. For example, the wireless communication system can use various multiple access schemes such as code division multiple access (CDMA), time division multiple access (TDMA), and frequency division multiple access (FDMA).
An orthogonal frequency division multiplexing (OFDM) scheme uses a plurality of orthogonal sub-carriers. Further, the OFDM scheme uses an orthogonality between inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT). A transmitter transmits data by performing IFFT. A receiver restores original data by performing FFT on a received signal. The transmitter uses IFFT to combine the plurality of sub-carriers, and the receiver uses FFT to split the plurality of sub-carriers. According to the OFDM scheme, complexity of the receiver can be reduced in a frequency selective fading environment of a broadband channel, and spectral efficiency can be improved through selective scheduling in a frequency domain by utilizing channel characteristics which are different from one subcarrier to another. An orthogonal frequency division multiple access (OFDMA) scheme is an OFDM-based multiple access scheme. According to the OFDMA scheme, a radio resource can be more efficiently used by allocating different subcarriers to multiple users.
The wireless communication system employs one or more base stations (BSs) having a coverage area. A typical BS can transmit multiple data streams for broadcast, multicast, and/or unicast services. The data stream denotes a stream of data that can be independently received by a user equipment (UE). In addition, the UE can also transmit the data stream to the BS or another UE.
Hereinafter, downlink is defined as transmission from the BS to the UE, and uplink is defined as transmission from the UE to the BS.
In general, the BS schedules radio resources. An uplink resource is a radio resource transmitted in uplink. A downlink resource is a radio resource transmitted in downlink. In downlink, the BS informs the UE of the downlink resource allocated to the data stream, and the UE receives the data stream through the downlink resource. In uplink, the BS informs the UE of the uplink resource allocated to the data stream, and the UE transmits the data stream through the uplink resource.
Radio resource allocation information has to be occasionally transmitted to the UE. This is because the UE should know the radio resource allocation information to transmit or receive the data stream. The radio resource allocation information is a control signal. The radio resource is transmitted through a dedicated control channel or a common control channel. The dedicated control channel denotes a control channel for at least one specific UE. The common control channel denotes a control channel for all UEs in the coverage area.
The radio resource may be allocated in a different size according to an amount of data streams to be transmitted, a channel condition, or a quality of service (QoS). When the amount of data streams increases, more radio resources have to be allocated. For effective use of the limited radio resources, the radio resources need to be adaptively allocated for data streams which change variously.
Accordingly, there is a need for a method capable of increasing efficiency of limited radio resources by adaptively allocating the radio resources in a wireless communication system.